is it possible to set a projector upside down on a high shelf... possibly adding some sort of feet on the corners to raise it an inch or so so that the top can vent? or is that somehow dangerous or bad for the projector.... has anyone ever done this???

Why would you do that when you can just sit it on a shelf right side up. Why even bother turning it upside down? What are you trying to do or am I missing the punch line?

The only reason I could think of is if a projector offered more lens shift in the "up" direction (away from the feet) than in the "down" direction, but the user didn't want to or couldn't ceiling mount it.

nevermind... i got it to work without having to flip it... i wanted to raise my shelf up higher to try and help with noise issues (it was too close to my head)... but because of where the door is in the room i have to place the PJ off center... it is an epson and the lens is on the far left of the unit... i was having trouble shifting the image down enough and over enough... by flipping it it would have moved the lens more toward the center... however i was able to get th eimage centered without having to do that by moving some things around and playing with the positioning

Why would you do that when you can just sit it on a shelf right side up. Why even bother turning it upside down? What are you trying to do or am I missing the punch line?

Many projectors cannot be used this way. In fact the only time you can have a projector right-side up, when mounted above the center line of the image, is with a good lens shift that works in BOTH directions. For instance the JVC's are +/- 80% so you can be 80% of the screen height above/below the center of the image while being upright/upsidedown. But for instance, a Infocus IN83 is a fixed 126% offset. That means when positioned above the screen, it HAS to be inverted to make the image work on the screen without tilting and keystoning.

To answer the question...it can be done, but some projectors produce a good amount of heat on the case which potentially could cause a problem. If you do it I would recommend proping it on some foam strips so that not all of the case is resting on the shelf.